Chronic mountain sickness

Chronic Mountain Sickness (CMS) is a disease that can develop during extended time living at a high altitude. It is also known as "Monge's Disease", after its first description in 1925 by Carlos Monge.[1] While acute mountain sickness is experienced shortly after ascent to high altitude, chronic mountain sickness may develop after many years of living at high altitude. In medicine, high altitude is defined as over 2500 metres (8200 ft), but most cases of CMS occur at over 3000 m (10000 ft). Recently it has been correlated with increased expression of the genes ANP32D and SENP1.[1]

Although CMS generally affects people native to altitudes higher than 3000m, it does not affect populations around the world equally. A recent study by Sahota and Panwar (2013)[2] reviewed CMS prevalence rates around the world and found the highest rates were found in Andean countries of South America and the lowest rates in people native to the East African Mountains of Ethiopia. CMS prevalence rates from the study are summarized below:

Ethiopia [3600m-4100m]: 0%

Tibetan Plateau (Tibetans): 0.91% to 1.2%

Indian Himalayas [3000m-4200m]: 4% to 7%

Kyrgyzstan [3000m-4200m]: 4.6%

Tibetan Plateau (Han Chinese): 5.6%

La Paz, Bolivia [3600m]: 6% to 8%

Bolivia: 8% to 10%

Cerro de Pasco, Peru [4300m]: 14.8% to 18.2%

CMS is characterised by polycythemia (with subsequent increased hematocrit) and hypoxemia which both improve on descent from altitude. CMS is believed to arise because of an excessive production of red blood cells, which increases the oxygen carrying capacity of the blood [2] but may cause increased blood viscosity and uneven blood flow through the lungs (V/Q mismatch). However, CMS is also considered an adaptation of pulmonary and heart disease to life under chronic hypoxia at altitude.[3]

Treatment involves descent from altitude, where the symptoms will diminish and the hematocrit return to normal slowly. Acute treatment at altitude involves bleeding (phlebotomy), removal of circulating blood, to reduce the hematocrit; however this is not ideal for extended periods. Carbonic anhydrase inhibitors have been shown to improve chronic mountain sickness by reducing erythropoitin and the resulting polycytemia, which resulted in better arterial O2 and lower heart rate.[3]